Avoid empty mtext before aligned

luamml-convert.lua

@@ -253,6 +253,7 @@ end
 
 local function noad_to_table(noad, sub, cur_style, joining)
   local nucleus, core = kernel_to_table(noad.nucleus, sub == noad_over and cur_style//2*2+1 or cur_style)
+  if not nucleus then return end
   if core and core[0] == 'mo' and core.minsize and not core.maxsize then
     core.maxsize = core.minsize -- This happens when a half-specified delimiter appears alone in a list.
                                 -- If it has a minimal size, it should be fixed to that size (since there is nothing bigger in it's list)

luamml-patches-amsmath.sty

@@ -9,7 +9,11 @@
     \nonmatherr@ { \begin { \@currenvir } }
   \fi
   \savecolumn@ % Assumption: called inside a group
+  \luamml_annotate:en {
+    nucleus = true, core = false
+  } {
     \alignedspace@left
+  }
   \ams@start@box {#1} \bgroup
     \maxfields@ #2 \relax
     \ifnum \maxfields@ > \m@ne